Orthopaedic knee prosthesis having controlled condylar curvature

ABSTRACT

An orthopaedic knee prosthesis includes a tibial bearing and a femoral component configured to articulate with the tibial bearing. The femoral component includes a posterior cam configured to contact a spine of the tibial bearing and a condyle surface curved in the sagittal plane. The radius of curvature of the condyle surface decreases gradually between early-flexion and mid-flexion. Additionally, in some embodiments, the radius of curvature of the condyle surface may be increased during mid-flexion.

This application is a continuation of Utility patent application Ser.No. 17/108,309, now U.S. Pat. No. 11,369,478, which was filed on Dec. 1,2020, which is a continuation of Utility patent application Ser. No.16/391,512, now U.S. Pat. No. 10,849,760, which was filed on Apr. 23,2019, which is a continuation of Utility patent application Ser. No.15/949,546, now U.S. Pat. No. 10,265,180, which was filed on Apr. 10,2018, which is a continuation of Utility patent application Ser. No.15/145,573, now U.S. Pat. No. 9,937,049, which was filed on May 3, 2016,which is a continuation of Utility patent application Ser. No.14/486,085, now U.S. Pat. No. 9,326,864, which was filed on Sep. 15,2014, which is a continuation of Utility patent application Ser. No.13/481,943, now U.S. Pat. No. 8,834,575, which was filed on May 28,2012, which is a continuation of U.S. patent application Ser. No.12/165,575, now U.S. Pat. No. 8,187,335, which was filed on Jun. 30,2008, the entirety of each of which is hereby incorporated by reference.

CROSS-REFERENCE TO RELATED U.S. PATENT APPLICATION

Cross-reference is made to U.S. Utility patent application Ser. No.12/165,579, now U.S. Pat. No. 8,828,086, entitled “Orthopaedic FemoralComponent Having Controlled Condylar Curvature” by John L. Williams etal., which was filed on Jun. 30, 2008; to U.S. Utility patentapplication Ser. No. 12/165,574, now U.S. Pat. No. 8,192,498 entitled“Posterior Cruciate-Retaining Orthopaedic Knee Prosthesis HavingControlled Condylar Curvature” by Christel M. Wagner, which was filed onJun. 30, 2008; to U.S. Utility patent application Ser. No. 12/165,582,now U.S. Pat. No. 8,206,451 entitled “Posterior Stabilized OrthopaedicProsthesis” by Joseph G. Wyss, which was filed on Jun. 30, 2008; and toU.S. Provisional Patent Application Ser. No. 61/077,124 entitled“Orthopaedic Knee Prosthesis Having Controlled Condylar Curvature” byJoseph G. Wyss, which was filed on Jun. 30, 2008; the entirety of eachof which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates generally to orthopaedic prostheses, andparticularly to orthopaedic prostheses for use in knee replacementsurgery.

BACKGROUND

Joint arthroplasty is a well-known surgical procedure by which adiseased and/or damaged natural joint is replaced by a prosthetic joint.A typical knee prosthesis includes a tibial tray, a femoral component,and a polymer insert or bearing positioned between the tibial tray andthe femoral component. Depending on the severity of the damage to thepatient's joint, orthopaedic prostheses of varying mobility may be used.For example, the knee prosthesis may include a “fixed” tibial bearing incases wherein it is desirable to limit the movement of the kneeprosthesis, such as when significant soft tissue damage or loss ispresent. Alternatively, the knee prosthesis may include a “mobile”tibial bearing in cases wherein a greater degree of freedom of movementis desired. Additionally, the knee prosthesis may be a total kneeprosthesis designed to replace the femoral-tibial interface of bothcondyles of the patient's femur or a uni-compartmental (or uni-condylar)knee prosthesis designed to replace the femoral-tibial interface of asingle condyle of the patient's femur.

The type of orthopedic knee prosthesis used to replace a patient'snatural knee may also depend on whether the patient's posterior cruciateligament is retained or sacrificed (i.e., removed) during surgery. Forexample, if the patient's posterior cruciate ligament is damaged,diseased, and/or otherwise removed during surgery, a posteriorstabilized knee prosthesis may be used to provide additional supportand/or control at later degrees of flexion. Alternatively, if theposterior cruciate ligament is intact, a cruciate retaining kneeprosthesis may be used.

Typical orthopaedic knee prostheses are generally designed to duplicatethe natural movement of the patient's joint. As the knee is flexed andextended, the femoral and tibial components articulate and undergocombinations of relative anterior-posterior motion and relativeinternal-external rotation. However, the patient's surrounding softtissue also impacts the kinematics and stability of the orthopaedic kneeprosthesis throughout the joint's range of motion. That is, forcesexerted on the orthopaedic components by the patient's soft tissue maycause unwanted or undesirable motion of the orthopaedic knee prosthesis.For example, the orthopaedic knee prosthesis may exhibit an amount ofunnatural (paradoxical) anterior translation as the femoral component ismoved through the range of flexion.

In a typical orthopaedic knee prosthesis, paradoxical anteriortranslation may occur at nearly any degree of flexion, but particularlyat mid to late degrees of flexion. Paradoxical anterior translation canbe generally defined as an abnormal relative movement of a femoralcomponent on a tibial bearing wherein the contact “point” between thefemoral component and the tibial bearing “slides” anteriorly withrespect to the tibial bearing. This paradoxical anterior translation mayresult in loss of joint stability, accelerated wear, abnormal kneekinematics, and/or cause the patient to experience a sensation ofinstability during some activities.

SUMMARY

According to one aspect, a posterior stabilized orthopaedic kneeprosthesis includes a femoral component and a tibial bearing. Thefemoral component may include a pair of spaced apart condyles definingan intracondylar notch therebetween. At least one of the pair of spacedapart condyles may have a condyle surface curved in the sagittal plane.The femoral component may also include a posterior cam positioned in theintracondylar notch. The tibial bearing may include a platform having abearing surface configured to articulate with the condyle surface of thefemoral component and a spine extending upwardly from the platform.

In some embodiments, the condyle surface of the femoral component maycontact the bearing surface at a first contact point on the condylesurface at a first degree of flexion, contact the bearing surface at asecond contact point on the condyle surface at a second degree offlexion, and contact the bearing surface at a third contact point on thecondyle surface at a third degree of flexion. Additionally, theposterior cam of the femoral component may contact the spine of thetibial bearing at a fourth degree of flexion.

The second degree of flexion may be greater than the first degree offlexion and may be in the range of about 0 degrees to about 50 degreesin some embodiments. For example, in one embodiment, the second degreeof flexion is no greater than about 30 degrees. The third degree offlexion may be greater than the second degree and less than about 90degrees. For example, in one embodiment, the third degree of flexion isat least 30 degrees. In another embodiment, the third degree of flexionis at least 50 degrees. In still another embodiment, the third degree offlexion is at least 70 degrees. In some embodiments, the fourth degreeof flexion is no greater than about 10 degrees more than the thirddegree of flexion. For example, in one particular embodiment, the fourthdegree of flexion is no greater than the third degree of flexion.Additionally, in some embodiments, the fourth degree of flexion is atleast 50 degrees. In another embodiment, the fourth degree of flexion isat least 70 degrees.

The condyle surface in the sagittal plane may have a first radius ofcurvature at the first contact point, a second radius of curvature atthe second contact point, and a third radius of curvature at the thirdcontact point. In some embodiments, the third radius of curvature isgreater than the second radius of curvature by at least 0.5 millimeters.For example, the third radius of curvature may be greater than thesecond radius of curvature by at least 2 millimeters in some embodimentsor 5 millimeters in other embodiments. Additionally, in someembodiments, the ratio of the second radius to the third radius is inthe range of 0.75 to 0.85.

In some embodiments, the condyle surface of the femoral component in thesagittal plane may include first curved surface section and a secondcurved surface section. The first curved surface section may be definedbetween the first contact point and the second contact point. The secondcurved surface section may be defined between the second contact pointand the third contact point. In such embodiments, the first curvedsurface section may have a substantially constant radius of curvaturesubstantially equal to the second radius of curvature. Additionally, thesecond curved surface section may have a substantially constant radiusof curvature substantially equal to the third radius of curvature.

According to another aspect, a posterior stabilized orthopaedic kneeprosthesis includes a femoral component and a tibial bearing. Thefemoral component may include a pair of spaced apart condyles definingan intracondylar notch therebetween. At least one of the pair of spacedapart condyles may have a condyle surface curved in the sagittal plane.The femoral component may also include a posterior cam positioned in theintracondylar notch. The tibial bearing may include a platform having abearing surface configured to articulate with the condyle surface of thefemoral component and a spine extending upwardly from the platform.

In some embodiments, the condyle surface of the femoral component maycontact the bearing surface at a first contact point on the condylesurface at a first degree of flexion. The first degree of flexion may beless than about 30 degrees. Additionally, the condyle surface maycontact the bearing surface at a second contact point on the condylesurface at a second degree of flexion. The second degree of flexion maybe in the range of 35 degrees to 90 degrees. The condyle surface of thefemoral component may also contact the bearing surface at a thirdcontact point on the condyle surface at a third degree of flexion. Thethird degree of flexion may be greater than the second degree offlexion. Additionally, the condyle surface may contact the bearingsurface at a plurality of contact points between the first contact pointand the second contact point when the femoral component is moved fromthe first degree of flexion to the second degree of flexion. Further, insome embodiments, the posterior cam of the femoral component may contactthe spine of the tibial bearing at a fourth degree of flexion. Thefourth degree of flexion at which the posterior cam contacts the spinemay be less than, substantially equal to, or slightly greater than thethird degree of flexion. For example, in one embodiment, the fourthdegree of flexion is no greater than about 10 degrees more than thethird degree of flexion.

In some embodiments, each contact point of the plurality of contactpoints is defined by a ray extending from a common origin to therespective contact point of the plurality of contact points. Each rayhas a length defined by the following polynomial equation:r_(θ)=(a+(b*θ)+(c*θ²)+(d*θ³)), wherein re is the length of the raydefining a contact point at θ degrees of flexion, a is a coefficientvalue between 20 and 50, and b is a coefficient value in a rangeselected from the group consisting of: −0.30<b<0.0, 0.00<b<0.30, andb=0. If bis in the range of −0.30<b<0.00, then c is a coefficient valuebetween 0.00 and 0.012 and d is a coefficient value between −0.00015 and0.00. Alternatively, if b is in the range of 0<b<0.30, then c is acoefficient value between −0.010 and 0.00 and d is a coefficient valuebetween −0.00015 and 0.00. Alternatively still, if b is equal to 0, thenc is a coefficient value in a range selected from the group consistingof: −0.0020<c<0.00 and 0.00<c<0.0025 and d is a coefficient valuebetween −0.00015 and 0.00. In some embodiments, the distance between theorigin of the first radius of curvature and the common origin of therays is in the range of 0 and 10 millimeters.

In some embodiments, the first degree of flexion may be in the range of0 degrees to 10 degrees, the second degree of flexion may be in therange of 45 degrees to 55 degrees, and the third degree of flexion maybe in the range of about 65 degrees to about 75 degrees. For example, inone particular embodiment, the first degree of flexion is about 0degrees, the second degree of flexion is about 50 degrees, and the thirddegree of flexion is about 70 degrees. Additionally, the fourth degreeof flexion may be about 70 degrees.

In some embodiments, the condyle surface in the sagittal plane has afirst radius of curvature at the first contact point, a second radius ofcurvature at the second contact point, and a third radius of curvatureat the third radius of curvature. In such embodiments, the third radiusof curvature is greater than the second radius of curvature by at least0.5 millimeters. In some embodiments, the third radius of curvature maybe greater than the first radius of curvature by at least 2 millimeters.Additionally, in some embodiments, the third radius of curvature isgreater than the first radius of curvature by at least 5 millimeters.

Additionally, in some embodiments, the condyle surface of the femoralcomponent in the sagittal plane may include a curved surface sectiondefined between the second contact point and the third contact point. Insuch embodiments, the curved surface section may have a substantiallyconstant radius of curvature substantially equal to the third radius ofcurvature.

According to yet another aspect, a posterior stabilized orthopaedic kneeprosthesis may include a posterior stabilized orthopaedic kneeprosthesis includes a femoral component and a tibial bearing. Thefemoral component may include a pair of spaced apart condyles definingan intracondylar notch therebetween. At least one of the pair of spacedapart condyles may have a condyle surface curved in the sagittal plane.The femoral component may also include a posterior cam positioned in theintracondylar notch. The tibial bearing may include a platform having abearing surface configured to articulate with the condyle surface of thefemoral component and a spine extending upwardly from the platform.

In some embodiments, the condyle surface of the femoral component maycontact the bearing surface at a first contact point on the condylesurface at a first degree of flexion. The first degree of flexion may beless than about 30 degrees. Additionally, the condyle surface maycontact the bearing surface at a second contact point on the condylesurface at a second degree of flexion. The second degree of flexion maybe in the range of 35 degrees to 90 degrees. The condyle surface of thefemoral component may also contact the bearing surface at a thirdcontact point on the condyle surface at a third degree of flexion. Thethird degree of flexion may be greater than the second degree offlexion. In some embodiments, the posterior cam of the femoral componentmay contact the spine of the tibial bearing at a fourth degree offlexion. Additionally, the condyle surface may contact the bearingsurface at a plurality of contact points between the first contact pointand the second contact point when the femoral component is moved fromthe first degree of flexion to the second degree of flexion. Further, insome embodiments, the posterior cam of the femoral component may contactthe spine of the tibial bearing at a fourth degree of flexion. Thefourth degree of flexion may be equal to or less than the third degreeof flexion.

In some embodiments, the condyle surface in the sagittal plane has afirst radius of curvature at the first contact point, a second radius ofcurvature at the second contact point, and a third radius of curvatureat the third radius of curvature. In such embodiments, the third radiusof curvature is greater than the second radius of curvature by at least2.0 millimeters.

Yet further, each contact point of the plurality of contact points maybe defined by a ray extending from a common origin to the respectivecontact point of the plurality of contact points. Each ray has a lengthdefined by the following polynomial equation:r_(θ)=(a+(b*θ)+(c*θ²)+(d*θ³)), wherein re is the length of the raydefining a contact point at 0 degrees of flexion, a is a coefficientvalue between 20 and 50, and b is a coefficient value in a rangeselected from the group consisting of: −0.30<b<0.0, 0.00<b<0.30, andb=0. If bis in the range of −0.30<b<0.00, then c is a coefficient valuebetween 0.00 and 0.012 and d is a coefficient value between −0.00015 and0.00. Alternatively, if b is in the range of 0<b<0.30, then c is acoefficient value between −0.010 and 0.00 and d is a coefficient valuebetween −0.00015 and 0.00. Alternatively still, if b is equal to 0, thenc is a coefficient value in a range selected from the group consistingof: −0.0020<c<0.00 and 0.00<c<0.0025 and d is a coefficient valuebetween −0.00015 and 0.00. In some embodiments, the distance between theorigin of the first radius of curvature and the common origin of therays is in the range of 0 and 10 millimeters.

Additionally, in some embodiments, each of the pair of spaced apartcondyles may include a condyle surface. In such embodiments, the condylesurfaces may be substantially symmetrical or may be asymmetrical.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description particularly refers to the following figures,in which:

FIG. 1 is an exploded perspective view of one embodiment of anorthopaedic knee prosthesis;

FIG. 2 is a cross-sectional view of a femoral component and tibialbearing of FIG. 1 taken generally along section lines 2-2 and having thefemoral component articulated to a first degree of flexion;

FIG. 3 is a cross-sectional view of a femoral component and tibialbearing of FIG. 2 having the femoral component articulated to a seconddegree of flexion;

FIG. 4 is a cross-sectional view of a femoral component and tibialbearing of FIG. 2 having the femoral component articulated to a thirddegree of flexion;

FIG. 5 is a cross-section view of one embodiment of the femoralcomponent of FIG. 1;

FIG. 6 is a cross-section view of another embodiment of the femoralcomponent of FIG. 1;

FIG. 7 is a cross-section view of another embodiment of the femoralcomponent of FIG. 1;

FIG. 8 is a cross-section view of another embodiment of the femoralcomponent of FIG. 1;

FIG. 9 is graph of the anterior-posterior translation of a simulatedfemoral component having an increased radius of curvature located atvarious degrees of flexion;

FIG. 10 is graph of the anterior-posterior translation of anothersimulated femoral component having an increased radius of curvaturelocated at various degrees of flexion;

FIG. 11 is graph of the anterior-posterior translation of anothersimulated femoral component having an increased radius of curvaturelocated at various degrees of flexion;

FIG. 12 is graph of the anterior-posterior translation of anothersimulated femoral component having an increased radius of curvaturelocated at various degrees of flexion;

FIG. 13 is a cross-sectional view of another embodiment of the femoralcomponent of FIG. 1;

FIG. 14 is a table of one embodiment of coefficient values of apolynomial equation defining the curve of the femoral component of FIG.13 for a family of femoral component sizes;

FIG. 15 is a table of one embodiment of radii of curvature values andratios for a family of femoral component sizes; and

FIG. 16 is a cross-section view of another condyle of another embodimentof the femoral component of FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

While the concepts of the present disclosure are susceptible to variousmodifications and alternative forms, specific exemplary embodimentsthereof have been shown by way of example in the drawings and willherein be described in detail. It should be understood, however, thatthere is no intent to limit the concepts of the present disclosure tothe particular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

Terms representing anatomical references, such as anterior, posterior,medial, lateral, superior, inferior, etcetera, may be used throughoutthis disclosure in reference to both the orthopaedic implants describedherein and a patient's natural anatomy. Such terms have well-understoodmeanings in both the study of anatomy and the field of orthopaedics. Useof such anatomical reference terms in the specification and claims isintended to be consistent with their well-understood meanings unlessnoted otherwise.

Referring now to FIG. 1, in one embodiment, a posterior stabilizedorthopaedic knee prosthesis 10 includes a femoral component 12, a tibialbearing 14, and a tibial tray 16. The femoral component 12 and thetibial tray 16 are illustratively formed from a metallic material suchas cobalt-chromium or titanium, but may be formed from other materials,such as a ceramic material, a polymer material, a bio-engineeredmaterial, or the like, in other embodiments. The tibial bearing 14 isillustratively formed from a polymer material such as a ultra-highmolecular weight polyethylene (UHMWPE), but may be formed from othermaterials, such as a ceramic material, a metallic material, abio-engineered material, or the like, in other embodiments.

As discussed in more detail below, the femoral component 12 isconfigured to articulate with the tibial bearing 14, which is configuredto be coupled with the tibial tray 16. The illustrative tibial bearing14 is embodied as a rotating or mobile tibial bearing and is configuredto rotate relative to the tibial tray 12 during use. However, in otherembodiments, the tibial bearing 14 may be embodied as a fixed tibialbearing, which may be limited or restricted from rotating relative thetibial tray 16.

The tibial tray 16 is configured to be secured to a surgically-preparedproximal end of a patient's tibia (not shown). The tibial tray 16 may besecured to the patient's tibia via use of bone adhesive or otherattachment means. The tibial tray 16 includes a platform 18 having antop surface 20 and a bottom surface 22. Illustratively, the top surface20 is generally planar and, in some embodiments, may be highly polished.The tibial tray 16 also includes a stem 24 extending downwardly from thebottom surface 22 of the platform 18. A cavity or bore 26 is defined inthe top surface 20 of the platform 18 and extends downwardly into thestem 24. The bore 26 is formed to receive a complimentary stem of thetibial insert 14 as discussed in more detail below.

As discussed above, the tibial bearing 14 is configured to be coupledwith the tibial tray 16. The tibial bearing 14 includes a platform 30having an upper bearing surface 32 and a bottom surface 34. In theillustrative embodiment wherein the tibial bearing 14 is embodied as arotating or mobile tibial bearing, the bearing 14 includes a stem 36extending downwardly from the bottom surface 32 of the platform 30. Whenthe tibial bearing 14 is coupled to the tibial tray 16, the stem 36 isreceived in the bore 26 of the tibial tray 16. In use, the tibialbearing 14 is configured to rotate about an axis defined by the stem 36relative to the tibial tray 16. In embodiments wherein the tibialbearing 14 is embodied as a fixed tibial bearing, the bearing 14 may ormay not include the stem 36 and/or may include other devices or featuresto secure the tibial bearing 14 to the tibial tray 18 in a non-rotatingconfiguration.

The upper bearing surface 32 of the tibial bearing 14 includes a medialbearing surface 42, a lateral bearing surface 44, and a spine 60extending upwardly from the platform 16. The medial and lateral bearingsurfaces 42, 44 are configured to receive or otherwise contactcorresponding medial and lateral condyles 52, 54 of the femoralcomponent 14 as discussed in more detail below. As such, each of thebearing surface 42, 44 has a concave contour. The spine 60 is positionedbetween the bearing surfaces 42, 44 and includes an anterior side 62 anda posterior side 64 having a cam surface 66. In the illustrativeembodiment, the cam surface 66 has a substantially concave curvature.However, spines 60 including cam surfaces 66 having other geometries maybe used in other embodiments. For example, a tibial bearing including aspine having a substantially “S”-shaped cross-sectional profile, such asthe tibial bearing described in U.S. patent application Ser. No.13/527,758, entitled “Posterior Stabilized Orthopaedic Prosthesis” byJoseph G. Wyss, et al., which is hereby incorporated by reference, maybe used in other embodiments.

The femoral component 12 is configured to be coupled to asurgically-prepared surface of the distal end of a patient's femur (notshown). The femoral component 12 may be secured to the patient's femurvia use of bone adhesive or other attachment means. The femoralcomponent 12 includes an outer, articulating surface 50 having a pair ofmedial and lateral condyles 52, 54. In use, the condyles 52, 54 replacethe natural condyles of the patient's femur and are configured toarticulate on the corresponding bearing surfaces 42, 44 of the platform30 of the tibial bearing 14.

The condyles 52, 54 are spaced apart to define an intracondyle notch orrecess 56 therebetween. A posterior cam 80 and an anterior cam 82 (seeFIG. 2) are positioned in the intracondyle notch 56. The posterior cam80 is located toward the posterior side of the femoral component 12 andincludes a cam surface 86 is configured to engage or otherwise contactthe cam surface 66 of the spine 60 of the tibial bearing 12 duringflexion as illustrated in and described in more detail below in regardto FIGS. 2-4.

It should be appreciated that the illustrative orthopaedic kneeprosthesis 10 is configured to replace a patient's right knee and, assuch, the bearing surface 42 and the condyle 52 are referred to as beingmedially located; and the bearing surface 44 and the condyle 54 arereferred to as being laterally located. However, in other embodiments,the orthopaedic knee prosthesis 10 may be configured to replace apatient's left knee. In such embodiments, it should be appreciated thatthe bearing surface 42 and the condyle 52 may be laterally located andthe bearing surface 44 and the condyle 54 may be medially located.Regardless, the features and concepts described herein may beincorporated in an orthopaedic knee prosthesis configured to replaceeither knee joint of a patient.

Referring now to FIGS. 2-4, the femoral component 12 is configured toarticulate on the tibial bearing 14 during use. Each condyle 52, 54 ofthe femoral component 12 includes a condyle surface 100, which isconvexly curved in the sagittal plane and configured to contact therespective bearing surface 42, 44. Additionally, during a predeterminedrange of flexion, the posterior cam 80 of the femoral component 12contacts the spine 60 of the tibial bearing 14. For example, in oneembodiment as shown in FIG. 2, when the orthopaedic knee prosthesis 10is in extension or is otherwise not in flexion (e.g., a flexion of about0 degrees), the condyle surface 100 of the condyle 52 contacts thebearing surface 42 (or bearing surface 44 in regard to condyle 54) atone or more contact points 100 on the condyle surface 100. Additionally,at this particular degree of flexion, the posterior cam 80 is not incontact with the spine 60. However, at later (i.e., larger) degrees offlexion, the posterior cam 80 is configured to contact the spine 60 toprovide an amount of control over the kinematics of the orthopaedicprosthesis.

As the orthopaedic knee prosthesis 10 is articulated through the middledegrees of flexion, the femoral component 12 contacts the tibial bearing14 at one or more contact points on the condyle surface 100. Forexample, in one embodiment as illustrated in FIG. 3, when theorthopaedic knee prosthesis 10 is articulated to a middle degree offlexion (e.g., at about 45 degrees), the condyle surface 100 contactsthe bearing surface 42 at one or more contact points 104 on the condylesurface 100. As discussed in more detail below, depending on theparticular embodiment, the posterior cam 80 may or may not be in contactwith the spine 60 at this particular degree of flexion. Regardless, asthe orthopaedic knee prosthesis 10 is articulated to a late degree offlexion (e.g., at about 70 degrees of flexion), the condyle surface 100contacts the bearing surface 42 at one or more contact points 106 on thecondyle surface 100 as illustrated in FIG. 4. Additionally, theposterior cam 80 is now in contact with the spine 60. It should beappreciated, of course, that the femoral component 12 may contact thetibial bearing 14 at a plurality of contact points on the condylesurface 100 at any one particular degree of flexion. However, forclarity of description, only the contact points 102, 104, 106 have beenillustrated in FIGS. 2-4, respectively.

The particular degree of flexion at which the posterior cam 80 initiallycontacts the spine 60 is based on the particular geometry of the condylesurface 100 of the femoral component 12. For example, in theillustrative embodiment of FIGS. 2-4, the orthopaedic knee prosthesis 10is configured such that the posterior cam 80 initially contacts thespine 60 at about 70 degrees of flexion. However, in other embodimentsthe posterior cam 80 may initially contact the spine 60 at other degreesof flexion as discussed in more detail below.

The orthopaedic knee prosthesis 10 is configured such that the amount ofparadoxical anterior translation of the femoral component 12 relative tothe tibial bearing 14 may be reduced or otherwise delayed to a later(i.e., larger) degree of flexion. In particular, as discussed in moredetail below, the condyle surface 100 of one or both of the condyles 52,54 has particular geometry or curvature configured to reduce and/ordelay anterior translations and, in some embodiments, promote“roll-back” or posterior translation, of the femoral component 12. Itshould be appreciated that by delaying the onset of paradoxical anteriortranslation of the femoral component 12 to a larger degree of flexion,the overall occurrence of paradoxical anterior translation may bereduced during those activities of a patient in which deep flexion isnot typically obtained.

In a typical orthopaedic knee prosthesis, paradoxical anteriortranslation may occur whenever the knee prosthesis is positioned at adegree of flexion greater than zero degrees. The likelihood of anteriortranslation generally increases as the orthopaedic knee prosthesis isarticulated to larger degrees of flexion, particularly in themid-flexion range. In such orientations, paradoxical anteriortranslation of the femoral component on the tibial bearing can occurwhenever the tangential (traction) force between the femoral componentand the tibial bearing fails to satisfy the following equation:

T<μN  (1)

wherein “T” is the tangential (traction) force, “μ” is the coefficientof friction of the femoral component and the tibial bearing, and “N” isthe normal force between the femoral component and the tibial bearing.As a generalization, the tangential (traction) force between the femoralcomponent and the tibial bearing can be defined as

T=M/R  (2)

wherein “T” is the tangential (traction) force between the femoralcomponent and the tibial bearing, “M” is the knee moment, and “R” is theradius of curvature in the sagittal plane of the condyle surface incontact with the tibial bearing at the particular degree of flexion. Itshould be appreciated that equation (2) is a simplification of thegoverning real-world equations, which does not consider such otherfactors as inertia and acceleration. Regardless, the equation (2)provides insight that paradoxical anterior translation of an orthopaedicknee prosthesis may be reduced or delayed by controlling the radius ofcurvature of the condyle surface of the femoral component. That is, bycontrolling the radius of curvature of the condyle surface (e.g.,increasing or maintaining the radius of curvature), the right-hand sideof equation (2) may be reduced, thereby decreasing the value of thetangential (traction) force and satisfying the equation (1). Asdiscussed above, by ensuring that the tangential (traction) forcesatisfies equation (1), paradoxical anterior translation of the femoralcomponent on the tibial bearing may be reduced or otherwise delayed to agreater degree of flexion.

Based on the above analysis, to reduce or delay the onset of paradoxicalanterior translation, the geometry of the condyle surface 100 of one orboth of the condyles 52, 54 of the femoral component 12 is controlled.For example, in some embodiments, the radius of curvature of the condylesurface 100 is controlled such that the radius of curvature is heldconstant over a range of degrees of flexion and/or is increased in theearly to mid flexion ranges. Comparatively, typical femoral componentshave decreasing radii of curvatures beginning at the distal radius ofcurvature (i.e., at about 0 degrees of flexion). However, it has beendetermined that by maintaining a relatively constant radius of curvature(i.e., not decreasing the radius of curvature) over a predeterminedrange of degrees of early to mid-flexion and/or increasing the radius ofcurvature over the predetermined range of degrees of flexion may reduceor delay paradoxical anterior translation of the femoral component 12.

Additionally, in some embodiments, the condyle surface 100 is configuredor designed such that the transition between discrete radii of curvatureof the condyle surface 100 is gradual. That is, by graduallytransitioning between the discrete radii of curvature, rather thanabrupt transitions, paradoxical anterior translation of the femoralcomponent 12 may be reduced or delayed. Further, in some embodiments,the rate of change in the radius of curvature of the condyle surface inthe early to mid flexion ranges (e.g., from about 0 degrees to about 90degrees) is controlled such that the rate of change is less than apredetermined threshold. That is, it has been determined that if therate of change of the radius of curvature of the condyle surface 100 isgreater than the predetermined threshold, paradoxical anteriortranslation may occur.

Accordingly, in some embodiments as illustrated in FIGS. 5-8, thecondyle surface 100 of the femoral component 12 has an increased radiusof curvature in early to middle degrees of flexion. By increasing theradius of curvature, paradoxical anterior translation may be reduced ordelayed to a later degree of flexion as discussed in more detail below.In particular, paradoxical anterior translation may be delayed to adegree of flexion at or beyond which the posterior cam 80 of the femoralcomponent 12 initially contacts the spine 60 of the tibial bearing 14.Once the posterior cam 80 is in contact with the spine 60, paradoxicalanterior translation is controlled by the engagement of the posteriorcam 80 to the spine 60. That is, the posterior cam 80 may be restrictedfrom moving anteriorly by the spine 60.

The amount of increase between the radius of curvature R2 and the radiusof curvature R3, as well as, the degree of flexion on the condylesurface 100 at which such increase occurs has been determined to affectthe occurrence of paradoxical anterior translation. As discussed in moredetail in the U.S. patent application Ser. No. 12/165,579, now U.S. Pat.No. 8,828,086, entitled “Orthopaedic Femoral Prosthesis HavingControlled Condylar Curvature”, which was filed concurrently herewithand is hereby incorporated by reference, multiple simulations of variousfemoral component designs were performed using the LifeMOD/Knee Sim,version 1007.1.0 Beta 16 software program, which is commerciallyavailable from LifeModeler, Inc. of San Clemente, Calif., to analyze theeffect of increasing the radius of curvature of the condyle surface ofthe femoral components in early and mid flexion. Based on such analysis,it has been determined that paradoxical anterior translation of thefemoral component relative to the tibial bearing may be reduced orotherwise delayed by increasing the radius of curvature of the condylesurface by an amount in the range of about 0.5 millimeters to about 5millimeters or more at a degree of flexion in the range of about 30degrees of flexion to about 90 degrees of flexion.

For example, the graph 200 illustrated in FIG. 9 presents the results ofa deep bending knee simulation using a femoral component wherein theradius of curvature of the condyle surface is increased by 0.5millimeters (i.e., from 25.0 millimeters to 25.5 millimeters) at 30degrees of flexion, at 50 degrees of flexion, at 70 degrees of flexion,and at 90 degrees of flexion. Similarly, the graph 300 illustrated inFIG. 10 presents the results of a deep bending knee simulation using afemoral component wherein the radius of curvature of the condyle surfaceis increased by 1.0 millimeters (i.e., from 25.0 millimeters to 26.0millimeters) at 30 degrees of flexion, at 50 degrees of flexion, at 70degrees of flexion, and at 90 degrees of flexion. The graph 400illustrated in FIG. 11 presents the results of a deep bending kneesimulation using a femoral component wherein the radius of curvature ofthe condyle surface is increased by 2.0 millimeters (i.e., from 25.0millimeters to 27.0 millimeters) at 30 degrees of flexion, at 50 degreesof flexion, at 70 degrees of flexion, and at 90 degrees of flexion.Additionally, the graph 500 illustrated in FIG. 12 presents the resultsof a deep bending knee simulation using a femoral component wherein theradius of curvature of the condyle surface is increased by 5.0millimeters (i.e., from 25.0 millimeters to 26.0 millimeters) at 30degrees of flexion, at 50 degrees of flexion, at 70 degrees of flexion,and at 90 degrees of flexion.

In the graphs 200, 300, 400, 500, the condylar lowest or most distalpoints (CLP) of the medial condyle (“med”) and the lateral condyle(“lat”) of the femoral component are graphed as a representation of therelative positioning of the femoral component to the tibial bearing. Assuch, a downwardly sloped line represents roll-back of the femoralcomponent on the tibial bearing and an upwardly sloped line representsanterior translation of the femoral component on the tibial bearing.

As illustrated in the graphs 200, 300, 400, 500, anterior sliding of thefemoral component was delayed until after about 100 degrees of flexionin each of the embodiments; and the amount of anterior translation waslimited to less than about 1 millimeter. In particular, “roll-back” ofthe femoral component on the tibial bearing was promoted by largerincreases in the radius of curvature of the condyle surface at earlierdegrees of flexion. Of course, amount of increase in the radius ofcurvature and the degree of flexion at which such increase is introducedis limited by other factors such as the anatomical joint space of thepatient's knee, the size of the tibial bearing, and the like.Regardless, based on the simulations reported in the graphs 200, 300,400, 500, paradoxical anterior translation of the femoral component onthe tibial bearing can be reduced or otherwise delayed by increasing theradius of curvature of the condyle surface of the femoral componentduring early to mid flexion.

Accordingly, referring back to FIGS. 5-8, the condyle surface 100 in thesagittal plane is formed in part from a number of curved surfacesections 102, 104, 106, 108 the sagittal ends of each of which aretangent to the sagittal ends of any adjacent curved surface section ofthe condyles surface 100. Each curved surface section 102, 104, 106, 108is defined by a radius of curvature. In particular, the curved surfacesection 102 is defined by a radius of curvature R2, the curved surfacesection 104 is defined by a radius of curvature R3, the curved surfacesection 106 is defined by a radius of curvature R4.

The condyle surface 100 of the femoral component 12 is configured suchthat the radius of curvature R3 of the curved surface section 104 isgreater than the radius of curvature R2 of the curved surface section102. In one embodiment, the radius of curvature R3 is greater than theradius of curvature R2 by 0.5 millimeters or more. In anotherembodiment, the radius of curvature R3 is greater than the radius ofcurvature R2 by 2 millimeters or more. In another embodiment, the radiusof curvature R3 is greater than the radius of curvature R2 by 2millimeters or more. In a particular embodiment, the radius of curvatureR3 is greater than the radius of curvature R2 by at least 5 millimetersor more. It should be appreciated, however, that the particular increaseof radius of curvature between R2 and R3 may be based on or scaled tothe particular size of the femoral component 12 in some embodiments.

Each of the curved surface sections 102, 104, 106, 108 contacts hebearing surface 42 (or 44) of the tibial bearing 14 through differentranges of degrees of flexion. For example, the curved surface section102 extends from an earlier degree of flexion θ1 to a later degree offlexion θ2. The curved surface section 104 extends from the degree offlexion θ2 to a later degree of flexion θ3. The curved surface section106 extends from the degree of flexion θ3 to a later degree of flexionθ4.

For example, in one embodiment, as illustrated in FIG. 5, the curvedsurface section 102 extends from a degree of flexion θ1 of about 0degrees of flexion to a degree of flexion θ2 of about 50 degrees offlexion. The curved surface section 104 extends from the degree offlexion θ2 of about 50 degrees of flexion to a degree of flexion θ3 ofabout 70 degrees of flexion. The curved surface section 106 extends fromthe degree of flexion θ3 of about 70 degrees of flexion to a degree offlexion θ4 of about 120 degrees of flexion. In the illustrativeembodiment of FIG. 5, the posterior cam 80 of the femoral component 12is configured to engage or contact the spine 60 of the tibial bearing 14at a degree of flexion θC of about 70 degrees of flexion. However, inother embodiments, the posterior cam 80 may be configured to engage thespine 60 at a degree of flexion earlier or later than 70 degrees. Byensuring the posterior cam 80 engages or contacts the spine 60 prior toor soon after the reduction in radius of curvature from R3 to R4, thecontrol of the kinematics of the orthopaedic prosthesis can betransitioned from the geometry of the condyle surface 100 to theinteraction of the posterior cam 80 and spine 60, which may furtherreduce the amount of anterior translation of the femoral component 12.For example, in one particular embodiment, the posterior cam 80 may beconfigured to engage or contact the spine 60 at a degree of flexion θCthat is no greater than 10 degrees more than the degree of flexion θ3 atwhich the radius curvature of the condyle surface 100 decreases from theradius of curvature R3 to the radius of curvature R4.

In another embodiment, as illustrated in FIG. 6, the curved surfacesection 102 extends from a degree of flexion θ1 of about 0 degrees offlexion to a degree of flexion θ2 of about 10 degrees of flexion. Thecurved surface section 104 extends from the degree of flexion θ2 ofabout 10 degrees of flexion to a degree of flexion θ3 of about 30degrees of flexion. The curved surface section 106 extends from thedegree of flexion θ3 of about 30 degrees of flexion to a degree offlexion θ4 of about 120 degrees of flexion. In the illustrativeembodiment of FIG. 6, the posterior cam 80 of the femoral component 12is configured to engage or contact the spine 60 of the tibial bearing 14at a degree of flexion θC of about 30 degrees of flexion. Again,however, the posterior cam 80 may be configured to engage the spine 60at a degree of flexion earlier than 30 degrees (i.e., earlier than thereduction in radius of curvature from R3 to R4) or soon thereafter(e.g., within 0-10 degrees) in other embodiments.

In another embodiment, as illustrated in FIG. 7, the curved surfacesection 102 extends from a degree of flexion θ1 of about 0 degrees offlexion to a degree of flexion θ2 of about 30 degrees of flexion. Thecurved surface section 104 extends from the degree of flexion θ2 ofabout 30 degrees of flexion to a degree of flexion θ3 of about 50degrees of flexion. The curved surface section 106 extends from thedegree of flexion θ3 of about 50 degrees of flexion to a degree offlexion θ4 of about 120 degrees of flexion. In the illustrativeembodiment of FIG. 7, the posterior cam 80 of the femoral component 12is configured to engage or contact the spine 60 of the tibial bearing 14at a degree of flexion θC of about 50 degrees of flexion. Again,however, the posterior cam 80 may be configured to engage the spine 60at a degree of flexion earlier than 50 degrees (i.e., earlier than thereduction in radius of curvature from R3 to R4) or soon thereafter(e.g., within 0-10 degrees) in other embodiments.

In another embodiment, as illustrated in FIG. 8, the curved surfacesection 102 extends from a degree of flexion θ1 of about 0 degrees offlexion to a degree of flexion θ2 of about 70 degrees of flexion. Thecurved surface section 104 extends from the degree of flexion θ2 ofabout 70 degrees of flexion to a degree of flexion θ3 of about 90degrees of flexion. The curved surface section 106 extends from thedegree of flexion θ3 of about 90 degrees of flexion to a degree offlexion θ4 of about 120 degrees of flexion. In the illustrativeembodiment of FIG. 8, the posterior cam 80 of the femoral component 12is configured to engage or contact the spine 60 of the tibial bearing 14at a degree of flexion θC of about 90 degrees of flexion. Again,however, the posterior cam 80 may be configured to engage the spine 60at a degree of flexion earlier than 90 degrees (i.e., earlier than thereduction in radius of curvature from R3 to R4) or soon thereafter(e.g., within 0-10 degrees) in other embodiments.

It should be appreciated that the embodiments of FIGS. 5-8 areillustrative embodiments and, in other embodiments, each of the curvedsurface sections 102, 104, 106 may extend from degrees of flexiondifferent from those shown and discussed above in regard to FIGS. 5-8.For example, in each of the embodiments of FIGS. 5-8, although thecurved surface section 102 is illustrated as beginning at about 0degrees of flexion, the curved surface section 102 may being at a degreeof flexion prior to 0 degrees of flexion (i.e., a degree ofhyperextension) in other embodiments.

Additionally, it should be appreciated that the degree of flexion OC atwhich the posterior cam 80 contacts the spine 60 may be less than,substantially equal to, or slightly greater than the degree of flexionθ3 at which the radius of curvature R3 decreases to the radius ofcurvature R4. In some embodiments, the degree of flexion θC is within apredetermined threshold of the degree of flexion θ3. For example, in oneparticular embodiment, the degree of flexion θC is within about 10degrees of the degree of flexion θ3. For example, the radius ofcurvature R3 may decrease to the radius of curvature R4 at a degree offlexion θ3 of about 70 degrees and the posterior cam 80 may beconfigured to initially contact the spine 60 at a degree of flexion θCof in the range of about 60 to about 80 degrees of flexion.

Referring now to FIGS. 13-15, in some embodiments, the condyle surface100 includes a gradual transition between discreet radii of curvature inthe early to mid flexion ranges such that the change in the radius ofcurvature of the condyle surface over a range of degrees of flexion isreduced. For example, as illustrated in FIG. 13, the curved surfacesection 102 in some embodiments is designed to provide a gradualtransition from the first radius of curvature R1 to the second radius ofcurvature R2. To do so, the curved surface section 102 is defined by aplurality of rays 120 rather than a constant radius of curvature asillustrated in and described above in regard to FIGS. 5-8. Each of theplurality of rays 120 originate from a common origin O. Additionally,each of the plurality of rays 120 defines a respective contact point 130on the curved surface section 120. Although only three rays 120 areillustrated in FIG. 13 for clarity of the drawing, it should beappreciated that an infinite number of rays 120 may be used to definethe curved surface section 102.

The location of each contact points 130, which collectively define thecurved surface section 102, can be determined based on the length ofeach ray 120 at each degree of flexion. In particular and unexpectedly,it has been determined that paradoxical anterior translation of thefemoral component 12 on the tibial bearing 14 may be reduced or delayedby defining the curved surface section 102 according to the followingpolynomial equation:

r _(θ)=(a+(b*θ)+(c*θ ²)+(d*θ ³)),  (3)

wherein “r_(θ)” is the length of a ray 120 (in metric units) defining acontact point 130 on the curved surface section 104 at “θ” degrees offlexion, “a” is a scalar value between 20 and 50, and “b” is acoefficient value selected such that:

−0.30<b<0.00,

0.00<b<0.30, or

b=0  (4)

If the selected coefficient “b” is in the range of −0.30<b<0.00, thencoefficients “c” and “d” are selected such that:

0.00<c<0.012, and

−0.00015<d<0.00.  (5)

Alternatively, if the selected coefficient “b” is in the range of0.00<b<0.30, then coefficients “c” and “d” are selected such that:

−0.010<c<0.00, and

−0.00015<d<0.00.  (6)

Further, if the selected coefficient “b” is equal to 0, thencoefficients “c” and “d” are selected such that:

−0.0020<c<0.00, or

0.00<c<0.0025, and

−0.00015<d<0.00.  (7)

It should be appreciated that ranges of values for the scalar “a” andcoefficients “b”, “c”, and “d” have been determined from an infinitenumber of possible solutions for the polynomial equation (3). That is,the particular set of ranges provided above have been determined togenerate a family of curves (i.e., the curved surface section 102) thatprovide a gradual transitioning of the condyle surface 100 from theradius of curvature R1 to the radius of curvature R2 such that anteriortranslation of the femoral component 12 relative to the tibial bearing14 is reduced or delayed. Additionally, it should be appreciated thatthe range of values for each coefficient “a”, “b”, “c”, and “d” areprovided above in regard to embodiments designed using the metric systemof units. However, such range of coefficient values may be converted foruse in embodiments using other systems of units such as the Englishsystem of units.

The overall shape of the curved surface section 102 is also affected bythe placement of the common origin O of the plurality of rays 120. Bylimiting the distance 124 between the common origin O of the pluralityof rays 120 and the origin 122 of the distal radius of curvature R1,paradoxical anterior sliding of the femoral component 12 on the tibialbearing 14 may be reduced or delayed. Additionally, stability of theorthopaedic knee prosthesis 10 may be improved by ensuring the commonorigin O of the plurality of rays 120 is within the predetermineddistance 124 from the origin 122 of the distal radius of curvature R1.As such, in one embodiment, the location of the common origin O of theplurality of rays 120 is selected such that the distance 124 between thecommon origin O and the origin 120 of the radius of curvature R1 is lessthan about 10 millimeters to reduce or delay anterior translation of thefemoral component and/or provide improved stability to the orthopaedicknee prosthesis 10.

It should be appreciated that the distance 124 between the common originO and the origin 122 of the radius of curvature R1 and the particularcoefficient values may be dependent upon the particular size of thefemoral component 12 in some embodiments. For example, as illustrated inFIG. 14, a table 700 illustrates one particular embodiment ofcoefficient values for the above-defined polynomial equation (3) andvalues for the distance 124 defined between the common origin O and theorigin 122 of the distal radius of curvature R1. As shown in table 700,the distance 124 between the common origin O and the origin 122 of theradius of curvature R1 and the value for the scalar “a” change acrossthe femoral component sizes. However, in this particular embodiment, thevalues for the coefficients “b”, “c”, and “d” are constant across thefemoral component sizes. It should be appreciated, however, that inother embodiments, the coefficient values “b”, “c”, and “d” may changeacross the femoral component sizes.

As discussed above, in some embodiments, the condyle surface 100 isfurther designed or configured such that the change in the radius ofcurvature of the condyle surface 100 in the early and mid flexion rangesis not too great or too abrupt (e.g., the ratio of the degree of changein radius of curvature to the change in degrees of flexion is toogreat). That is, if the ratio of the radius of curvature R1 to theradius of curvature R2, R3, or R4 is too great, paradoxical anteriortranslation of the femoral component 12 may occur. As such, by designingthe condyle surface 100 of the femoral component 12 such that the ratiosof the distal radius of curvature R1 to (i) the radius of curvature R2of the curved surface section 102, (ii) the radius of curvature R3 ofthe curved surface section 104, and (iii) the radius of curvature R4 ofthe late flexion curved surface section 106 are less than apredetermined threshold value, paradoxical anterior sliding mayunexpectedly be reduced or otherwise delayed.

Accordingly, in one particular embodiment, the condyle surface 100 ofthe femoral component 12 is designed such that the ratio of the radiusof curvature of R1 to the radius of curvature of R2 is between about1.10 to about 1.30, the ratio of the radius of curvature of R1 to theradius of curvature R3 is between about 1.001 to about 1.100, and theratio of the radius of curvature of R1 to the radius of curvature R4 isabout 1.25 to about 2.50. Further, in some embodiments, the ratio of theradius of curvature of R2 to the radius of curvature of R3 is betweenabout 0.74 and about 0.85.

It should be appreciated that the particular amount of increase in theradius of curvature R2 to R3 of the condyle surface 100 of the femoralcomponent 12 and/or the positioning of such increase on the condylesurface 100 may also be based on, scaled, or otherwise affected by thesize of the femoral component 12. That is, it should be appreciated thatan increase of the radius of curvature R2 to R3 of the condyle surface100 of 0.5 millimeters is a relatively larger increase in small-sizedfemoral components compared to larger-sized femoral components. As such,the magnitude of the increase in the radius of curvature R2 to R3 of thecondyle surface 100 of the femoral component 12 may change acrossfemoral component sizes. In one embodiment, however, the ratios of theradius of curvatures R1 to the radius of curvatures R2, R3, and R4 aremaintained at a substantially constant value across the family offemoral component sizes.

For example, as illustrated in FIG. 15, a table 800 defines the lengthof each radius of curvature R1, R2, R3, R4 for a family of femoralcomponent sizes 1 through 10. As illustrated in the table 850, thelength of each radius of curvature R1, R2, R3, R4 for each size 1-10 ofthe femoral component 12 is selected such that the ratios of R1/R2 andR1/R3 are substantially constant across the femoral component sizes. Inthe illustrative embodiment, as previously discussed, the ratio of theradius of curvature R1 to the radius of curvature R2 is maintained at avalue of about 1.25 to about 1.27 across the femoral component sizes 1through 10 and the ratio of the radius of curvature R1 to the radius ofcurvature R3 is maintained at a value of about 1.005 across the femoralcomponent sizes 1 through 10.

The overall shape and design of the condyle surface 100 of the femoralcomponent 12 has been described above in regard to a single condyle 52,54 of the femoral component 12. It should be appreciated that in someembodiments both condyles 52, 54 of the femoral component 12 may besymmetrical and have similar condyle surfaces 100. However, in otherembodiments, the condyles 52, 54 of the femoral component 12 may beasymmetrical. For example, as illustrated in FIG. 16, the femoralcomponent 12 may include a second condyle 52, 54 having a condylesurface 300, which is defined in part by a plurality of curved surfacesections 302, 304, 306. The curved surface section 302 extends from anearlier degree of flexion θ5 to a later degree of flexion θ6. The curvedsurface section 304 extends from the degree of flexion θ6 to a laterdegree of flexion θ7. The curved surface section 306 extends from thedegree of flexion θ7 to a later degree of flexion θ8. The condylesurface 300 also includes a distal radius R5, which is graduallytransitioned to a radius of curvature R6 via the curved surface section302. Additionally, the curved section 304 is defined by a radius ofcurvature R7 and the curved section 306 is defined by a radius ofcurvature R8.

As such, in embodiments wherein the condyles 52, 54 are symmetrical, thedegree of flexion θ5 is substantially equal to the degree of flexion θ1,the degree of flexion θ6 is substantially equal to the degree of flexionθ2, the degree of flexion θ7 is substantially equal to the degree offlexion θ3, and the degree of flexion θ8 is substantially equal to thedegree of flexion θ4. Additionally, the radius of curvature R5 issubstantially equal to the radius of curvature R1, the radius ofcurvature R6 is substantially equal to the radius of curvature R2, theradius of curvature R7 is substantially equal to the radius of curvatureR3, and the radius of curvature R8 is substantially equal to the radiusof curvature R4. Further, the set of coefficient values “a”, b”, “c”,and/or “d” of the equation (4) described above are substantially similarfor both condyles.

However, in other embodiments, the condyles 52, 54 are asymmetrical. Assuch, the degree of flexion θ5 may be different from the degree offlexion θ1. Additionally, the degree of flexion θ6 may be different fromthe degree of flexion θ2. That is, the increase in radius of curvaturebetween R2 and R3 may occur at different degrees of flexion between thecondyles 52, 54. Further, the degree of flexion θ8 may be different fromthe degree of flexion θ4. It should be appreciated, however, that thedegree of flexion θ7 may be substantially equal to the degree of flexionθ3 such that the posterior cam 80 is positioned properly within theintracondylar notch 56.

Additionally, in those embodiments wherein the condyles 52, 54 areasymmetrical, the radius of curvature R5 may be different from theradius of curvature R1, the radius of curvature R6 may be different fromthe radius of curvature R2, the radius of curvature R7 may be differentfrom the radius of curvature R3, and/or the radius of curvature R8 maybe different from the radius of curvature R4. Further, the set ofcoefficient values “a”, b″, “c”, and/or “d” of the equation (3)described above may be different between the condyle surfaces 100 and300.

While the disclosure has been illustrated and described in detail in thedrawings and foregoing description, such an illustration and descriptionis to be considered as exemplary and not restrictive in character, itbeing understood that only illustrative embodiments have been shown anddescribed and that all changes and modifications that come within thespirit of the disclosure are desired to be protected.

There are a plurality of advantages of the present disclosure arisingfrom the various features of the devices and assemblies describedherein. It will be noted that alternative embodiments of the devices andassemblies of the present disclosure may not include all of the featuresdescribed yet still benefit from at least some of the advantages of suchfeatures. Those of ordinary skill in the art may readily devise theirown implementations of the devices and assemblies that incorporate oneor more of the features of the present invention and fall within thespirit and scope of the present disclosure as defined by the appendedclaims.

1. An orthopaedic knee prosthesis comprising: a femoral component havinga medial condyle surface curved in the sagittal plane and a lateralcondyle surface curved in the sagittal plane; and a tibial bearinghaving a medial bearing surface corresponding to and configured toarticulate with the medial condyle surface of the femoral component anda lateral bearing surface corresponding to and configured to articulatewith the lateral condyle surface of the femoral component, wherein themedial condyle surface (i) contacts the medial bearing surface at afirst contact point on the medial condyle surface at a first degree offlexion, the first degree of flexion being less than 30 degrees, and(ii) contacts the medial bearing surface at a second contact point onthe medial condyle surface at a second degree of flexion, the seconddegree of flexion being greater than the first degree of flexion,wherein the lateral condyle surface (i) contacts the lateral bearingsurface at a first point on the lateral condyle surface at a thirddegree of flexion, the third degree of flexion being less than 30degrees and the third degree of flexion being different from the firstdegree of flexion, and (ii) contacts the lateral bearing surface at asecond point on the lateral condyle surface at a fourth degree offlexion, the fourth degree of flexion being greater than the thirddegree of flexion, wherein the medial condyle surface is shaped suchthat in the sagittal plane the medial condyle surface (i) has a firstradius of curvature at the first contact point on the medial condylesurface, and (ii) has a second radius of curvature at the second contactpoint on the medial condyle surface different from the first radius ofcurvature, and wherein the lateral condyle surface is shaped such thatin the sagittal plane the lateral condyle surface (i) has a third radiusof curvature at the first contact point on the lateral condyle surface,the third radius of curvature being different than the first radius ofcurvature, and (ii) has a fourth radius of curvature at the secondcontact point on the lateral condyle surface, the fourth radius ofcurvature being different from the second radius of curvature and thethird radius of curvature, wherein the medial condyle surface has aplurality of radii of curvature between the first contact point and thesecond contact point on the medial condyle surface to transition fromthe first radius of curvature to the second radius of curvature over arange of flexion, and wherein the lateral condyle surface has aplurality of radii of curvature between the first contact point and thesecond contact point on the lateral condyle surface to transition fromthe third radius of curvature to the fourth radius of curvature over arange of flexion.